I am finishing up a two day inspection of two Gun Boat Rudders at the Hinckley Yard in Stuart, FL.
I used multiple forms of NDT; tap testing, thermal imaging and ultrasound (UT). For heating the rudders for the thermal imaging I used infrared lamps that are made for paint and resin curing. These lamps a great for this use, they heat evenly and slowly.
It is very important not to rely on just one form of inspection. Using multiple inspection techniques is how you can see the "big picture". I start out with thermal imaging, which I then process in software. This allows me to locate the anomalies that I will be using tap testing and UT to confirm.
Often it is possible to use an iPad with the software to due the processing on the job site. This is a way I can confirm what I see in the camera is an anomaly and then use the camera's built in later pointer to mark the anomaly.
How do you go about determining what the condition of your embedded chainplates are in? There is not a magic window we can peer into. Two options are to X Ray the chainplates and Thermal Imaging. Since I have not seen the X Ray images in person I can not give much comment. From what I have seen posted online, I am skeptical if it can pick up on the hair line cracks that can form in the stainless. With Thermal Imaging we can not see the chain plate per-say, but see the trapped moisture. If salt water is trapped against the stainless then crevice corrosion can begin.
In the January 2014 edition of Boat US Seaworthy magazine there was an alert written to inform the boat owner of this type of inspection and the concern of embedded chainplates.
Link To the Boat US Alert:
I was able to follow the removal of the chainplates and inspect them after the were removed. Four out of the six suffered from crevice corrosion.
I have also done an inspection on an Irwin that had trapped moisture and the owner reported that the chainplates, when removed did not have any corrosion. Most likely this boat had only fresh water trapped around the chainplates.
Image from the exterior indicating trapped moisture.
On a recent trip to Trinidad for a survey I was pleasantly surprised with the services available for the boat owner there. This is not the Caribbean Island you might be used to. You will not find an island crowded with tourists or your typical anchorages. In Chaguaramas you will find an assortment of boat yards and chandleries. My survey was at Peake Yacht Services where I found the staff to be very helpful. This yard is capable of repairs on any type of yacht. If you find yourself in Trinidad make sure you hire Jesse James as your taxi driver. Jesse is a true friend to the cruiser and he and his drivers will take good care of you. http://www.membersonlymaxitaxi.com/about.htm